Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1456—Removing acid components
  • B01D53/1475—Removing carbon dioxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/50—Carbon dioxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
  • F25J3/0223—H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis gas
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0252—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of hydrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0266—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of carbon dioxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
  • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/40—Processes or apparatus using other separation and/or other processing means using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/50—Processes or apparatus using other separation and/or other processing means using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2215/00—Processes characterised by the type or other details of the product stream
  • F25J2215/04—Recovery of liquid products
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
  • F25J2220/80—Separating impurities from carbon dioxide, e.g. H2O or water-soluble contaminants
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
  • F25J2230/30—Compression of the feed stream
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
  • F25J2230/32—Compression of the product stream
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
  • F25J2230/80—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being carbon dioxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

• the present invention relates to a method for recovery of carbon dioxide from a gas and uses thereof. More particular, the present invention re ⁇ lates to a two-step method for recovery of carbon di ⁇ oxide by condensation at a temperature close to but above the triple point of carbon dioxide and a subse ⁇ quent absorption of the gaseous carbon dioxide, which were not liquefied during condensation.
• the present invention also relates to a plant for the recovery of carbon dioxide from a gas.
• Carbon dioxide is a well-known gas, which is present in the atmosphere. It is released to the at ⁇ mosphere in large amounts by fermentation processes, limestone calcination, and all forms of combustion processes of carbon and carbon compounds. In the re ⁇ cent decades, the attention in respect of said emis ⁇ sion has been rising, because of the environmental problem due to future climate change via Greenhouse effect. Consequently, extensive work has been per- formed over the years in order to develop processes for the removal of carbon dioxide from combustion gases. If possible, a subsequent recovery of carbon dioxide may make those processes economical feasible.
• a method for liquefaction of carbon dioxide from fermentation of . alcohol or from other gas sources by condensation following compression is dis ⁇ closed in European patent application EP 1308502.
• the condensation takes place preferably at -20°C to -55°C and at a pressure in the range of 19-20 bar.
• no further effort for recovery of uncondensed carbon dioxide is mentioned in said script .
• the object of the present invention is to pro- "vide a method for recovery of carbon dioxide from a CO 2 -containing gas.
• an improved method for recovery of carbon diox ⁇ ide from a gas may be obtained by a novel two-step method.
• an initial condensation of the gas to be treated with a subsequent absorption of the gaseous carbon dioxide, which did not condense in the first step it is possible to recover carbon dioxide at much higher yields than known in the art and in a financially more feasible way.
• the present invention relates to a method for recovery of carbon dioxide from a gas, use of said method, and a plant for recovery of carbon dioxide from a gas.
• the method according to the present invention comprises the steps of: a. feeding a plant with a pressurised C0 2 -containing gas and/or compressing the CO 2 -containing gas dur ⁇ ing feeding, b. cooling the compressed gas obtained in step a, c. separating the gas obtained in step b, by use of a condensation procedure by which said gas is sepa ⁇ rated into a CO 2 -rich liquid (Ll) and a CO 2 - containing gas (Gl) , d. absorbing the gas Gl obtained in step c by means of an absorbing agent, by which the gas Gl is sepa ⁇ rated into a liquid (L2) and a C0 2 -poor gas (G2) , e.
• the carbon dioxide is recovered substantially in two steps. Initially, carbon dioxide is recovered by con- densation of the compressed and cooled feed gas. Af ⁇ ter this gas/liquid separation, the carbon dioxide left in the gas stream is recovered by subjecting said gas stream to an absorption procedure, by which the carbon dioxide present in the gas is absorbed by means of an absorbing agent. Subsequent separation of the carbon dioxide and the absorbing agent yields a second crop of carbon dioxide.
• a pressure is ap ⁇ plied to the feeding gas unless the gas is already at a sufficient elevated pressure prior to feeding.
• the gas is pressurised during feeding in such a way that the pressure is at least 20 bar.
• the gas entering the plant is at an elevated pressure of at least 20 bar.
• the concentration of carbon dioxide in the feed gas will depend on the origin of said gas. However, in a preferred embodiment, the concentration of car ⁇ bon dioxide is at least 40 % v/v, more preferred at least 45 % v/v, and even more preferred at least 50 % v/v.
• step b of the method according to the inven ⁇ tion the compressed gas is cooled until an appropri ⁇ ate temperature has been reached. As mentioned above it is preferred that the temperature is kept above
• the gas is cooled until a temperature below -20°C has been reached.
• This cooling may be performed in one or more steps.
• the gas which is now present at an elevated pressure and a decreased temperature, is separated in step c by use of a condensation procedure into a CO 2 - rich liquid (Ll) and a C0 2 -containing gas (Gl) .
• said condensation procedure is a flash distillation.
• C0 2 -rich liquid as used herein is meant a liquid phase, wherein the con ⁇ tent of liquid CO 2 is at least 95 weight-%, more pre ⁇ ferred at least 97 weight-%, even more preferred at least 98.5 weight-%.
• the flash distillation is performed at a pressure by which condensation of 50 to 65 % of the carbon dioxide in the gas is recovered.
• the temperature of the C0 2 -containing gas GI leaving the flash distillation column is in the range of -3O 0 C to -7O 0 C, more preferred from -44.1 0 C to -56 0 C, even more preferred from -46.1 0 C to -50.1 0 C, most preferred from -47.6°C to -48.6°C, and the pres ⁇ sure of said gas is in the range of 10 bar to 200 "bar, more preferred from 12 bar to 50 bar, even more preferred from 20 bar to 40 bar, most preferred from 28 bar to 32 bar.
• the temperature of the liquid Ll leaving the flash distillation column is in the range of -3O 0 C to -55 0 C, more preferred from -45°C to -53°C, even more preferred from -47°C to -51°C, most pre- ferred from -48.5 0 C to -49.5 0 C, and the pressure of said liquid is in the range of 10 bar to 200 bar, more preferred from 14 bar to 27 bar, more preferred from 16 bar to 22 bar, most preferred from 17.5 bar to 18.5 bar.
• the liquid stream Ll may be cooled to a temperature below -55°C causing the carbon dioxide to solidify, and consequently removing the product of carbon dioxide from the plant as solid dry ice.
• step d In said flash distillation step more than half of the amount of the carbon dioxide present is recov- ered in the C0 2 -rich liquid. However, a considerable amount of carbon dioxide is leaving the flash distil ⁇ lation column in the cold gas stream Gl. In order to recover said considerable amount of carbon dioxide the cold gas stream Gl is passed through an absorp- tion column in step d.
• the gas ' Gl is sepa ⁇ rated into a liquid (L2) containing the major part (that is more than 90%) of the carbon dioxide enter ⁇ ing the absorption column and a CO 2 -poor gas (G2) .
• C0 2 -poor gas as used herein is meant a gas, in which the partial pressure of carbon dioxide is less than 3 bar, preferably less than 1.5 bar, more preferred less than 1 bar.
• the absorbing agent used for absorption of gaseous carbon dioxide may be any solvent known to be able to absorb carbon dioxide. However, it is pre ⁇ ferred to use an absorbing agent causing a physical absorption, rather than a chemical absorption, of carbon dioxide due to the lower energy consumption needed for the subsequent separation of carbon diox ⁇ ide from the absorption agent.
• preferred absorbing agents are SELEXOL, methanol, and propylene carbonate. At present, the most preferred absorbing agent is methanol. This is due to the fact that the absorption properties of methanol increase with de ⁇ creasing temperature. Consequently, no heating of the cold gas Gl is required prior to the absorption step. Furthermore, the energy requirement in the subsequent flash distillation is minimised.
• the temperature of the liquid L2, when leaving the absorption column, depends on the absorbing agent used.
• the temperature of methanol entering the absorption col ⁇ umn is in the range of -44°C to -52 0 C, more preferred from -46°C to -5O 0 C, and even more preferred around
• the temperature of SELEXOL when entering the absorption column is in the range of 0 0 C to 10 0 C, more preferred from 2°C to 8°C, and even more preferred from 4°C to 6 0 C.
• the temperature of the liquid L2 - is in the range of -23.7°C to -31.7 0 C, more preferred from -25.7 0 C to -29.7°C, most preferred from -27.2°C to -28.2 0 C, and the pressure of said liquid is in the range of 26 bar to 50 bar, more preferred from 28 bar to 45 bar, most preferred from 29.5 bar to 30.5 bar.
• the temperature of the liquid L2 is in the range 5°C to 20 0 C, more preferred from 1O 0 C to 17 0 C, even more preferred in the range of 12°C to 15°C.
• the liquid (L2) is preferably flash distilled in the subsequent step e of the proc ⁇ ess according to the invention.
• This separation may be performed in one or more consecutive flash- distillation columns.
• the flash distil ⁇ lation may be performed as a low pressure process or as a high pressure process or a combination of both. It is within the knowledge of a skilled person to combine the number, size and type of flash distilla ⁇ tion columns in order to obtain the combination most feasible.
• the temperature of the CO 2 - containing gas G3 when leaving the flash distillation column is in the range of -23.5°C to -33.5°C, more preferred from -25.5 0 C to -31.5°C, most preferred from -27.5 0 C to -29.5 0 C.
• the pressure of said gas is in the range of 5 bar to 20 bar in cases where the gas G3 is leaving a high pressure column and in the range of a negative pressure of 0.5 bar to a pressure of 3 bar when leaving a low pressure column.
• the gas leaving the flash distillation col- umn(s) is subsequently compressed (step f) . It is standard procedure for a skilled person to determine the number and size of compressors necessary in order to perform this compression step in the most suitable way. If more than one flash distillation column is used, the gas leaving each column may be compressed separately before mixing. Alternatively, the gases leaving each column may be mixed before compressing.
• the temperature of the gas G4 when enter- ing the distillation column, is in the range of -44°C to -52°C, more preferred from -46°C to -50°C, most preferred from -47.5 0 C to -48.5°C, and the pressure of said liquid is in the range of 14 bar to 22 bar, more preferred from 16 bar to 20 bar, most preferred from 17.5 bar 18.5 bar.
• the liquid L3 leaving the flash distillation column(s) in step e is substantially composed of ab ⁇ sorbing agent, wherein a low concentration of carbon dioxide is present. If no reuse of the absorbing agent is provided for, large amounts of absorbing agent must be disposed of. Thus, in a preferred em ⁇ bodiment said liquid is re-circulated to the absorp ⁇ tion column. As a result, the waste of absorbing agent is reduced significantly and the recovery of carbon dioxide is increased.
• the gas G4 contains absorbing agent in small amounts when entering the distillation column if no special effort for removing this impurity has been made. Therefore, in a preferred embodiment the traces of absorbing agent are removed from the liquid ob ⁇ tained in step f by a filtration method.
• the liquid Ll and the gas G4 obtained in step c and step f, respectively, may be distilled in order to purify the liquid carbon dioxide. Said two streams may be mixed inside the distillation column, or they may be distilled separately, and then mixed before storage. If filtration of the gas G4 as described ' above is included in the method this filtration step takes place prior to the distillation.
• the gases G2 and G5 obtained from the absorption column in step d and the above-mentioned distillation column(s) , respectively, are either recycled or is disposed of by burning.
• said gases are expanded prior to burning in order to recover energy.
• the purity of the liquid carbon dioxide L5 leaving the distillation column(s) will depend on the process parameters in each step of the method. Condi ⁇ tional upon the subsequent use of the product differ ⁇ ent grades of purity is required. If, for example, the subsequent use is the incorporation of carbon di ⁇ oxide as a component in a food product, the liquid carbon dioxide must be substantially absolute pure. By contrast, if the subsequent use is in a fire ex ⁇ tinguisher the requirements towards purity is less stringent. However, in a preferred embodiment the product is at least 99.5% pure. Examples of preferred uses of the produced liq ⁇ uid carbon dioxide are the incorporation as a food grade component in soft drinks and other food prod ⁇ ucts .
• Carbon dioxide may be recovered from all kinds of gases.
• all gases with a partial pres ⁇ sure of carbon dioxide above a certain value in order for the carbon dioxide to be condensed and in a mix ⁇ ture of components, which after condensation may be separated by distillation, can be treated in the method according to the present invention.
• the feeding C0 2 -containing gas is a waste gas originating from a plant for the manufacture of hydrogen and the gases G2 and G5 is recycled to said plant for manufacture of hydrogen.
• the present invention also relates to a plant for the recovery of carbon dioxide from a gas stream.
• a plant shown in the form of a flow diagram in figure 1
• a plant comprises optionally a compressor (A) con ⁇ nected to a cooling unit (B) , said cooling unit being connected to a condensation unit (C) having a gas outlet and a liquid outlet, the gas outlet of said condensation unit (C) being connected to an absorp- tion column (D) with a gas outlet and a liquid out ⁇ let, said outlet for liquid being connected to one or more consecutive separation units (E) each having a gas outlet and a liquid outlet, the gas outlets of _ said separation units (E) , being connected to one or more compressors (F) , and the outlet of said compres ⁇ sor(s) (F) and the outlet of the liquid outlet from the condensation unit (C) optionally being connected to one or more distillation columns (G) .
• the compressors A and F may be any kind of compressor suitable for compressing the gas to be treated.
• suitable compres ⁇ sors centrifugal, screw, and reciprocating compres ⁇ sors may be mentioned.
• Especially preferred compres- sors are those having high polytropic efficiency and thereby low power consumption.
• the cooling unit B may be any kind of refrig ⁇ erator capable of cooling a pressurised gas.
• a person skilled in the art can easily select a suitable cool ⁇ ing unit dependent on the required temperature to be reached and the chemical composition of the gas to be treated.
• the condensation unit (C) and the separation unit(s) (E) are preferably flash distillation col ⁇ umns.
• Said columns may be any kind of flash distilla ⁇ tion columns known in the art.
• a skilled person may easily determine whether one or more high pressure flash distillation column(s) or one or more low pres- sure distillation column(s) or a combination thereof is needed in order to obtain the result required in each step. It will also be within the knowledge of the skilled person to determine whether the desired result is achieved most suitable by using only one column, or by using two or more columns connected in series or in parallel.
• the absorption column (D) to be used may be any column known in the art suitable for the performance of absorbing gaseous carbon dioxide into an absorbing agent.
• the most suitable absorption columns to be used are normally packed columns with a low pressure drop, but also trayed columns may be employed.
• the plant comprises a dehydrator in order to remove water from the gaseous stream.
• a dehydrator in order to remove water from the gaseous stream.
• the process of dehydrating a gaseous stream is well-known in the art, and a suitable dehydrator to perform the dehydration is easily selected by the skilled person.
• dehydration units TSA ad- sorber with molecular sieves are preferably employed.
• the plant according to the present invention further comprises a filter for removal of traces of absorbing agent. It is within the knowledge of a skilled person to select the most appropriate kind of filter when the parame ⁇ ters such as type of absorbing agent as well as the temperature and pressure of the liquid to be fil ⁇ trated are known. Examples of preferred filters are filter units TSA adsorber with molecular sieves or activated carbon.
• the distillation column(s) (G) may be any kind of column known in the art suitable for distilling liquid carbon dioxide.
• the most suitable distillation columns to be used are normally packed columns with a low pressure drop, but also trayed columns may " be em ⁇ ployed.
• the gases G2 and G5 may be expanded before they are disposed of by burning in order to recover energy. Actually, an energy recovery about of 8-10% is possible. Consequently, a preferred embodiment is directed to the plant comprising an ex ⁇ pander for this purpose.
• a turbo expander, for gener ⁇ ating electrical energy or direct compression is .an example of a suitable expander, which may be used in the plant.
• FIG. 2 An alternative plant for performing the recov ⁇ ery of carbon dioxide from a gas stream according to the present invention is shown in figure 2.
• the plant shown in figure 2 differs from the plant shown in figure 1 in the way that no distilla ⁇ tion of the gas stream G4 occurs, and that said gas stream G4 is recycled and mixed with the pressurised - feeding stream prior to the optional dehydrator unit .
• the gas stream G5 leaving the distillation col ⁇ umn G' is recycled and mixed with the pressurised feeding stream after the optional dehydrator unit.
• the gas stream G2 is recycled. In a pre ⁇ ferred embodiment the gas stream G2 is recycled to the plant for the manufacture of hydrogen.
• FIG. 1 depicts a schematic flow diagram for the CO 2 recovery according to the present invention.
• the gas fed to the plant is a PSA off gas, which comes from a hydrogen plant.
• the gas enters the plant at a temperature of about 30°C, and a pressure of about 1.3 bar.
• the mass flow of the feeding stream is about 34440 kg/hr in total, wherein the mass flow of carbon dioxide amounts to 26760 kg/hr.
• the further chemical components are water (163 kg/hr) , methane
• the gas is compressed in a turbo compressor. After compression the gas is entering the dehydrator at a pressure of 31 bar and a temperature of 10 0 C, the lower temperature being a result of a pre-cooling of the compressed gas.
• the dehydrator which is of the type Activated alumina/molecular sieve TSA adsorber, water is removed to such an ex ⁇ tent that the content in the gas leaving the dehydra ⁇ tor is not detectable.
• the gas is cooled to a temperature about -39 0 C.
• a refrigeration plant is employed for this cooling procedure.
• This refrigeration plant is a cascade system with CO 2 /NH 3 as refrigerant.
• the CO 2 loop cools to -48°C and the NH 3 loop cools to
• - umn is a simple knock out drum.
• the carbon dioxide is divided into a liquid stream (Ll) and a gas stream (Gl) .
• Liquid carbon dioxide (Ll) is leaving the flash distillation column at a pressure of 18 bar and a temperature of -49°C with a mass flow of 14378 kg/hr and only containing traces of methane (118 kg/hr) and hydrogen, nitrogen, and carbon monoxide in even smaller amounts.
• these traces of impurities are removed to such an extent as being non-detectable in the liquid leaving the column.
• G 1 packed dis- tillation column
• the mass flow of carbon dioxide in the gas stream leaving said flash distillation column (C) amounts to 12382 kg/hr.
• This carbon dioxide is recov ⁇ ered in a subsequent absorption procedure using methanol as the absorbing agent. More precisely, the absorbing agent is a grade AA methanol having a water content of 0.1 %.
• the absorption column (D) is a packed column. The carbon dioxide is leaving the ab ⁇ sorption column either in the gas phase (G2) or as an absorbed component in the liquid phase (L2) .
• the gas phase (G2) is leaving the column (D) at a pressure of 18 bar and a temperature of -5O 0 C.
• the mass flow of carbon dioxide in the gas phase is only 919 kg/hr, while the mass flow of methane is 2177 kg/hr.
• the liquid phase (L2) is leaving the column
• the liquid phase L2 is subsequently flash dis ⁇ tilled in two consecutive flash distillation columns.
• the first column (E) is a high pressure column and the second column (E 1 ) is a low pressure column.
• carbon dioxide is flashed at elevated pressure to recover carbon dioxide to the inter stage pressure of the compressor, and hereby minimising the energy consumption.
• This column is a packed column.
• the residual carbon dioxide is recov ⁇ ered by flashing at a lower pressure.
• the solvent is re-boiled to ensure a high recovery of carbon dioxide at the top of the absorber and thereby ensure low residual carbon dioxide in the liquid. It is also possible to use a vacuum flash in order to further reduce the amount of carbon dioxide in the liquid.
• the pressure and the temperature of the gas G3 as well as of the liquid L3 leaving the high pressure flash column is 7 bar and -30°C, respectively.
• the mass flows are given in the table.
• the liquid phase L3 is passed on to the low pressure flash distilla- tion column (E 1 ) .
• the pressure and the temperature of the gas (G3 ' ) leaving the low pressure column is 1.2 bar and -45°C.
• the liquid phase leaving the low pres ⁇ sure column is recycled to the absorption column in order to reuse the methanol . At the same time the carbon dioxide left in said liquid phase is not wasted but returned to the absorption column.
• the gas stream leaving the low pressure column is compressed before mixed with the gas stream leav ⁇ ing the high pressure column. Subsequently the mix- ture of said two gases is further compressed in order to obtain a pressure of 23 bar at a temperature of 30°C before said mixture is entering the filtration unit in order to remove traces of methanol. Actually, in this preferred embodiment the concentration of methanol is decreased to such an extent that it can ⁇ not be detected in the stream leaving the filtration unit.
• a molecular sieve TSA adsorber is used as fil- ter, while the compressors are oil lubricated screw compressors.
• the filtrated liquid stream is passed on to a distillation column (G) at a pressure of 18 bar and a temperature of -49 0 C.
• the liquid leaving this distil ⁇ lation column (G) is mixed with the liquid leaving the distillation column (G 1 ) before storage.
• the mass flow of carbon dioxide in this streams (G+G 1 ) is 24578 kg/hr and equals the total mass stream as it does not contain any detectable impurities.
• the gases leaving the two distillation columns are mixed before they are entered into a turbo ex ⁇ pander. Also the gas leaving the absorber G2 is en ⁇ tered into the turbo expander. The gas leaving the turbo expander is disposed of by burning. The purpose of expanding said gases is to recover energy. In this preferred embodiment an energy recovery of 3 % was obtained. Cold and hot streams not described are used for energy minimisation.

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